The proposed research is designed to evaluate the functional importance of several putative telomere end-binding protein is budding yeast. The initial approach to be pursued is biochemical, namely, the purification of chromosomal terminus complexes (CTCs) by a combination of digestion with various nucleases, size exclusion chromatography, and selection on an anti-Rap1p immuno-affinity column. Co-purification of epitope tagged versions of candidate telomere end-binding proteins will be followed as a function of the cell cycle and mutations in the corresponding genes. In addition, genetic interactions between Cdc13p, Rif6p, and Est1p will be examined.